How to tell if a file was renamed between two commits

I'm trying to write a little utility that will extract all the revisions of a particular file. I start with a git rev-list HEAD -- filename, get the tree objects with git cat-file commit, the file objects with git ls-tree, and finally the file contents themselves with git cat-file blob. It works, except in the case where the file name was changed. git rev-list is smart enough to track those name changes, but my little revision tracker isn't. It dies when suddenly there is no file with the right name in the tree.

So... is there an easy way to work around this? Is there a way to get, say, rev-list to tell me when the file it is tracking changed names? Or a git-diff incantation? I just need something that will tell me given two commits and a file name whether the file was renamed between those two commits and if so what its new name is. There must be an easy way to do this, but I can't figure out what it is.

Thanks, rg